[VP,Integer,#1] Vector-predicated integer intrinsics

Summary:
This patch adds IR intrinsics for vector-predicated integer arithmetic.

It is subpatch #1 of the [integer
slice](https://reviews.llvm.org/D57504#1732277) of
[LLVM-VP](https://reviews.llvm.org/D57504).  LLVM-VP is a larger effort to bring
native vector predication to LLVM.

Reviewed By: andrew.w.kaylor

Differential Revision: https://reviews.llvm.org/D69891